Combined heat exchanging and fluid mixing apparatus

ABSTRACT

A combined heat exchanging and fluid mixing apparatus including a first conduit ( 44 ) for guiding a cool fluid through the first conduit and a second conduit ( 55 ) for guiding a hot gas through the second conduit. A heat conductive element ( 2 ) is arranged between the first conduit ( 44 ) and the second conduit ( 55 ) for transferring heat from the hot gas to the cool fluid. The apparatus further includes a third conduit ( 45 ) for guiding an exhaust fluid. The third conduit ( 45 ) comprises an exhaust fluid inlet ( 46 ) for introducing an exhaust fluid into the apparatus for mixing of the exhaust fluid with the hot gas and for a chemical reaction of the so formed exhaust fluid/hot gas mixture in the second conduit ( 55 ).

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of European PatentApplication No. 12188099, filed on Oct. 11, 2012, which is herebyincorporated herein by reference.

TECHNICAL FIELD

The invention relates to the field of combined heat exchanging and fluidmixing apparatuses.

BACKGROUND

Fluid mixers are well known for example in the field of exhaust systemsof motor vehicles. To enable a catalytic reaction of exhaust gas in acatalytic converter, a reducing agent, typically ammonia or urea, ismixed with the exhaust gas. For example in US 2002116916, upstream of acatalytic converter, grids are arranged next to an injection device forinjecting the reducing agent. The grids provide an even distribution ofthe exhaust gas/reducing agent mixture. While fluid mixers and catalyticconverters in exhaust systems are primarily used to remove noxiouscomponents, such as nitrogen oxides from the exhaust gas, catalyticreactions of exhaust gases may also be used to use up remaining fuelleft in the exhaust gas. If reaction heat produced in this process isused, energy efficiency of a system may be enhanced.

Fuel cells are known as energy converters with high efficiency. In fuelcells, for example hydrocarbon fuels are directly converted intoelectrical energy and heat. In order to enhance an overall efficiency ofan energy system the heat produced in the fuel cell may further be usedfor heating. Especially fuel cells operating at high temperatures, suchas solid oxide fuel cells (SOFC), are suitable candidates forapplication in combined power generation and heat recovery devices. Ingeneral, a heat exchanger is arranged downstream of the fuel cellheating up a cool fluid for further use. For operation, SOFCs need apreheated oxidizing gas, especially air. This gas may be preheated inthe heat exchanger before it is introduced into the SOFC. Furthermore,if a fuel introduced into the fuel cell is not completely used up such adepleted fuel leaving the fuel cell still contains fuel. The depletedfuel may now be mixed in a fluid mixer with the hot air leaving the SOFCfor oxidizing the depleted fuel/hot air mixture. The mixture is thenguided into the heat exchanger. The heat from the hot air as well as thereaction heat from the oxidizing reaction is used in the heat exchanger.Unfortunately, such systems include several individual components thatrequire space and have high production costs, for example a separatefluid mixer and a separate heat exchanger. Another example consists of aseparate burner and a separate heat exchanger, whereas the depleted fuelis mixed and oxidized in the said separate burner, which is placedupstream of the separate heat exchanger.

SUMMARY

Therefore, there is provided a heat exchanging and fluid mixingapparatus that takes into account disadvantages of the state of the art.Especially, there is provided a combined heat exchanging and fluidmixing apparatus that is weight and space saving and allows for reducedproduction costs.

The combined heat exchanging and fluid mixing apparatus according to thepresent invention comprises:

-   -   a first conduit for guiding a cool fluid through the first        conduit, the first conduit comprising a cool fluid inlet and a        cool fluid outlet;    -   a second conduit for guiding a hot gas through the second        conduit, the second conduit comprising a hot gas inlet and a hot        gas outlet;    -   a heat conductive element arranged between the first conduit and        the second conduit for transferring heat from the hot gas to the        cool fluid, the heat conductive element having a length defining        a maximum longitudinal extension for a heat exchanging process        in the apparatus; further comprising    -   a third conduit for guiding an exhaust fluid, the third conduit        comprising an exhaust fluid inlet for introducing the exhaust        fluid into the apparatus for mixing of the exhaust fluid with        the hot gas and for a chemical reaction of the so formed exhaust        fluid/hot gas mixture in the second conduit, wherein the third        conduit is provided with more than one openings for introducing        the exhaust fluid from the third conduit into the second        conduit, wherein the more than one openings for introducing the        exhaust fluid into the second conduit are arranged within the        maximum longitudinal extension for a heat exchanging process in        the apparatus, and wherein the more than one openings are        arranged substantially at a same longitudinal position with        respect to the second conduit.

A first conduit for guiding a cool fluid and a second conduit forguiding a hot fluid separated by a heat conductive element are arrangedfor a heat exchanging process from the hot gas to the cool fluid.Thereby, the length of the heat conductive element defines a maximumlongitudinal extension, where a heat exchanging process may take placein the apparatus. Such a maximum longitudinal extension may effectivelybe used for a heat exchange from the hot gas to the cool fluid if thefirst and the second conduits are arranged along the whole length of theheat conductive element.

By providing a third conduit with an exhaust fluid inlet at one endthereof for introducing an exhaust fluid into the apparatus and into thesecond conduit, fluid mixing is integrated into a heat exchanger. Byarranging more than one openings in the third conduit for introducingthe exhaust fluid from the third conduit into the second conduit withinthe maximum longitudinal extension for a heat exchanging process in theapparatus, the exhaust fluid is introduced into the second conduit, atthe earliest in a region inside the apparatus, where heat exchangingmight take place. A mixing of exhaust fluid and hot gas starts at thesame time or later, respectively further downstream (downstream withrespect to the hot gas inlet and the flow of the hot gas in the secondconduit) than the heat exchanging process from the hot gas to the coolfluid starts. To start the mixing for example when some heat has alreadybeen transferred from the hot gas to the cool fluid, may be favorable ifthe temperatures of the hot gas are very high at the hot gas inlet andrapid chemical reaction, for example oxidation of the exhaust fluid, andespecially excess heat generation by an exothermic chemical reaction,such as for example an oxidation process, shall be prevented or reduced.By additionally arranging the more than one openings at substantially asame longitudinal position with respect to the second conduit, a furthercontrolled chemical reaction and further controlled heat exchange may beperformed in the apparatus according to the invention. If more than oneopenings are arranged at substantially a same longitudinal position ofthe second conduit, each fluid injected into the second conduitinitially encounters the same hot gas environment. In addition, if theopenings are arranged substantially at a same longitudinal position,also further reaction conditions may be unified for the injected fluid.For example, a time when the injected fluid reaches a catalyticallyactive section in the second conduit or a time the injected fluid mixedwith the hot gas encounters the effect of the cooling by the cool fluidof the first conduit may substantially be the same for fluid injectedthrough different openings. By a catalytically active element a chemicalreaction may be triggered to occur or start at a specific longitudinalposition or region in the second conduit. By these measures, a firstconduit comprising a cooling fluid may be arranged and the temperatureof the cooling fluid may be adapted such that the chemical reaction andheat production in the second conduit is kept at a maximum or at adesired level. Substantially a same longitudinal position of theopenings with respect to the second channel generally corresponds to asubstantially same length or distance measured from an inlet of thesecond channel. However, in second conduits having one or more bends, asame longitudinal position essentially corresponds to a line, which isperpendicular to lateral conduit walls or to the flow direction in thesecond conduit.

If openings are arranged at different longitudinal positions in thesecond conduit it might occur that the fluid or mixture injected at amore upstream position already reacts before this fluid or mixturepasses the more downstream holes, and before it reaches a catalyticallyactive section in the second conduit. It may also occur that is reactsbefore it encounters the effect of the cooling by the cool fluid of thefirst conduit. If the reaction is exothermal, then excessive heat isproduced and such an overheated injected fluid or mixture reacts withfluid injected at a more downstream position. This may lead to forexample the burning of an injected exhaust fluid, which may damage theapparatus up to its destruction. With the arrangement of the openings asdescribed it may be accomplished that combustion of an injected exhaustfluid/hot gas mixture only occurs in a cooled area of the apparatus.

By combining fluid mixing and heat exchanging, no separate componentssuch as an individual fluid mixer arranged upstream of a heat exchangerare required. This reduces production and manufacturing costs, since noseparate devices have to be manufactured and assembled. In addition,both processes—the heat exchanging and the fluid mixing—are combined inone apparatus. Therefore, also one housing only is required, which may,for example, be a steel envelope. This further reduces material costsand weight and in addition space may be saved, especially also since noconnecting tubes are needed between individual components that arecombined in the apparatus according to the invention.

The terms ‘hot gas’ and ‘cool fluid’ are herein used to describe a gasand a fluid—which fluid may be a gas, a liquid or a mixture thereof—thatallow for a heat transfer from the hot gas to the cool fluid in a heatexchanger. The temperature of the cool fluid is lower than that of thehot gas. While there are basically no limitations as to a temperaturedifference between or a temperature range of the hot gas and the coolfluid, in some preferred embodiments, the temperature of the ‘hot gas’at the hot gas inlet is in a range between 500 and 1000 degrees Celsius,for example around 800 degrees Celsius. In some preferred embodimentsthe temperature of the cool fluid at the cool fluid inlet is ambienttemperature and a few hundred degrees Celsius, for example 700 degreesCelsius, at the cool fluid outlet.

An exhaust fluid may be a gas, a liquid or a gas-liquid-mixture. Mixingmay be supported by the design of the exhaust fluid inlet or the morethan one openings. For example the openings may act as nozzles, ormixing elements may be provided in the second conduit, for examplegrids, deflection elements or other obstacles causing turbulences in theflow of exhaust fluid and hot gas. An exhaust fluid is for example adepleted fuel from a fuel cell or an exhaust gas of an engine of a motorvehicle.

In preferred embodiments, a chemical reaction is an oxidation of theexhaust fluid, for example oxidation of a fuel. It may be, for example,a catalytic partial oxidation process (CPDX) of an exhaust fluid. AlsoCPDX is an exothermic chemical reaction. Therein, a fuel-air mixture ispartially combusted, so that a gas rich in hydrogen is formed. Thisexample for a chemical reaction that may occur in the apparatusaccording to the invention can for example be used to generate hydrogenfor the working of a fuel cell in a single device. Other examples ofchemical reactions are reforming processes of fuels, preferably ofhydrocarbons. These chemical reactions are mentioned by way of exampleonly. Further chemical reactions may depend on the content of theexhaust fluid as well as of the composition of the hot gas.

The energy required for starting and upkeeping a chemical reaction,especially an oxidation reaction of the exhaust fluid in the hot gas maybe delivered by the hot gas only. Heat gained by the oxidation processor by another exothermic process further supports the oxidation processor the other chemical reaction taking place in the second conduit.Reaction heat may also heat up the hot gas, which is then—together withthe hot gas—used in the heat exchanging process to heat up the coolfluid in the first conduit

The term “arranged within the maximum longitudinal extension for a heatexchanging process in the apparatus” is not limited to a feature, forexample to the more than one openings being arranged in the heatconductive element itself. The term rather describes a region in theapparatus, which region is in one dimension (or length) limited by thelength of the heat conductive element. A location of a feature being“arranged within the maximum longitudinal extension” is therefore notarranged in an area outside (only with respect of the longitudinaldirection) of the two longitudinal ends of the heat conductive elementbut within this region, for example parallel to the heat conductiveelement.

The more than one openings may be arranged in the heat conductiveelement, for example constructed as holes in a heat conductive plate, orparallel to the heat conductive element, for example arranged in a wallof a separate conduit guiding the exhaust fluid, which wall is not(necessarily) part of the heat conductive element. Preferably, the morethan one openings are arranged downstream of the hot gas inlet. Inpreferred embodiments of the apparatus according to the invention, aplurality of openings is arranged along a length of the third conduit.For example, the plurality of openings may be arranged across a width orpart of the width of the apparatus, such as the width or part of thewidth of the heat conductive plate.

The provision of more than one or a plurality of openings in the thirdconduit supports a mixing of the exhaust fluid passing through saidplurality of openings: the exhaust fluid is guided into the hot gas atseveral locations. By additionally arranging the plurality of openingsalong the length of the third conduit, the exhaust fluid is guided intothe hot gas at locations arranged along the length of the third conduit,which may be the width or part of the width of the apparatus, forexample the width or part of the width of a heat conductive element orheat conductive plate or an entire width of a second conduit. Forexample, one row of holes of a size of about 1 mm may be arranged evenlyover preferably an entire width of the second conduit. For example, onerow of ten or twenty holes may be arranged at a same longitudinalposition with respect to the second conduit.

According to an aspect of the apparatus according to the invention, theexhaust fluid inlet is arranged within the maximum longitudinalextension for a heat exchanging process in the apparatus. By this, notonly the more than one openings but also the exhaust fluid inlet isarranged within the maximum longitudinal extension. The exhaust fluidinlet is favorably arranged parallel to the heat conductive element, forexample at one end of the maximum longitudinal extension close to thehot gas inlet or versus the center of the maximum longitudinal extensionor between the one end and the center. Thus, the exhaust fluid may beintroduced into the apparatus at a position, where a heat transfer fromthe hot gas may already have started. This may be advantageous, in thatthe exhaust fluid may already have been heated up through the heatconductive element, in that a heat transfer to the cool fluid hasalready cooled down the hot gas and rapid oxidation or other exothermicchemical reaction of exhaust gas is prevented or minimized, in that theapparatus may be constructed in a compact manner, or by a combination ofthe aforementioned advantages.

The exhaust fluid is led into the apparatus at the exhaust fluid inletand is guided in the third conduit to the more than one openings of thethird conduit. The more than one openings may be arranged downstream ofthe hot gas inlet such that an exhaust fluid is directly introduced intohot gas and a mixing of exhaust fluid and hot gas occurs immediatelyupon introduction of the exhaust fluid into the second conduit. The flowof the hot gas carries the exhaust fluid along the flow direction of thehot gas in the second conduit.

In an aspect of the apparatus according to the invention, the thirdconduit is arranged in a direction perpendicular to a direction of thefirst or second conduit. With a perpendicular arrangement of the thirdconduit to either the first conduit or the second conduit or both aspace saving arrangement of the third conduit in or next to a first orsecond conduit may be achieved. The third conduit may be arranged in theapparatus without or without noticeably shortening the length of thefirst or second conduit, respectively. In addition, a perpendiculararrangement allows for the provision of a plurality of openingsextending across a width or part of the width of the apparatus and forthe introduction of exhaust fluid into the hot gas along a whole widthor part of the width of the second conduit, thereby supporting themixing of exhaust fluid and hot gas. If third conduit and second conduitare arranged perpendicular to each other, a line of openings arrangedalong the length of the third conduit is at the same time arranged at asame longitudinal position of the second conduit. By such anarrangement, manufacturing of the individual elements of the apparatusaccording to the invention is facilitated.

According to an aspect of the apparatus according to the invention, thefirst conduit and the third conduit are arranged on a same side of theheat conductive element and the more than one openings for the passingof the exhaust fluid from the third conduit into the second conduit isarranged in the heat conductive element. By this arrangement, the coolfluid and the exhaust fluid are guided on a same side of the heatconductive element in the respective first and third conduits. Separateconduits for the cool fluid and the exhaust fluid can be realized bysimple constructional means. In addition, the exhaust fluid may beintroduced into the apparatus on the ‘cool’ side of the heat exchanger,preventing or limiting a chemical reaction, especially an exothermicchemical reaction such as for example oxidation before mixing of theexhaust fluid with the hot gas. By passing the exhaust fluid throughmore than one openings in the heat conductive element, the secondconduit may be devoid of any obstructions. Due to the low density of thehot gas such obstructions in the second conduit might lead to a pressuredrop over the second conduit.

Between the first conduit and the third conduit a fluid-tight separationelement may be arranged for a fluid-tight separation of the firstconduit and the third conduit. The first and third conduits arepreferably arranged adjacent to each other and separated only by thefluid-tight separation element such that no fluid is exchanged from thefirst to the third conduit or vice versa. A separation element may be aspacer, for example in the form of a bar. Such a spacer may also definea dimension of the conduits, for example the height or thickness of theconduits.

According to another aspect of the apparatus according to the invention,the second conduit and the third conduit are arranged on a same side ofthe heat conductive element. Such an arrangement provides flexibility inthe location of the more than one openings, where exhaust fluid entersthe second conduit and actually mixes with the hot gas. For example, byarranging the third conduit more or less downstream of the hot gasinlet, for example adjacent the hot gas inlet or near half the length ofthe second conduit, a heat transfer and a reaction process may beoptimized. If the third conduit is arranged further downstream of thehot gas inlet, the temperature of the hot gas has already cooled down.Thereby, a temperature for an exothermic chemical reaction may be heldin a desired range. Also, the temperature of the hot gas at the hot gasinlet may be higher without causing excess chemical reactions already atthe exhaust fluid inlet or at the more than one openings.

In addition, by arranging the third conduit and the second conduit onthe same side of the heat conductive element, a first conduit forguiding the cool fluid may be extended. It may especially be extended toessentially a complete length of an apparatus, such that for example thewhole length of the heat conductive element may be used for the heatexchanging process.

According to a further aspect of the apparatus according to theinvention, the heat conductive element is a heat conductive platearranged between a first and a second side plate. The heat conductiveplate and the first and second side plates are arranged at a distance toeach other forming a first gap between the first side plate and the heatconductive plate and forming a second gap between the heat conductiveplate and the second side plate.

Plate heat exchangers are very effective due to their large surfaceareas useable for heat transfer. The manufacture of plate arrangementsis convenient and may easily be extended to multiple-stacks. Inaddition, by providing two conduits on one side of the heat exchangingplate and one conduit on the opposite side of the heat exchanging plate,no further plates for conduits for an additional or separatecooling/heating or for a separate exhaust gas flow is required. Thissimplifies a manufacturing and make the apparatus according to theinvention very compact.

In one embodiment according to this aspect the first gap is separated bythe fluid-tight separation element into the first conduit and the thirdconduit. The second conduit is formed by the second gap and the morethan one openings are arranged in the heat conductive plate. In thefirst gap being separated by the fluid-tight separation element, onepart the gap forms the first conduit and another part of the gap formsthe third conduit. In order for the exhaust fluid to pass from one sideof the heat conductive plate to the other side of the heat conductiveplate into the hot gas in the second conduit, the more than one openingsare arranged in the heat conductive plate. In this arrangement thesecond gap forms the second conduit. Therein the hot gas may flow,essentially undisturbed, from the hot gas inlet to the hot gas outlet.

A third conduit may also be integrated into a first conduit. By this, afirst conduit may extend over the length or part of the length of theheat conductive element.

In another embodiment according to this aspect the first conduit isformed by the first gap and the second conduit is formed by the secondgap, while the third conduit is arranged in the second conduit.Integrating the third conduit into the second conduit allows providing asecond conduit having a same length than without the presence of a thirdconduit in the second conduit, which length favorably corresponds to thelength of the heat conductive plate. Hot gas then flows past the thirdconduit, which may cause turbulences and support a mixing of exhaustfluid released from the third conduit with the hot gas in the secondconduit.

According to a further aspect of the apparatus according to theinvention, the second conduit comprises a catalytically active elementfor a further chemical reaction such as an oxidation of the exhaustfluid/hot gas mixture.

To further support the chemical reaction such as an oxidation process ofthe exhaust fluid/hot gas mixture—or in case the temperature of the hotgas is not sufficient for a chemical reaction or to completely react theexhaust fluid—, a catalytically active element may be arranged in thesecond conduit. Such a catalytically active element may be arranged in alimited area of the second conduit and may be arranged downstream of theexhaust fluid inlet and especially downstream of the more than oneopenings. A catalytically active element is preferably arranged such,for example in a middle portion of the second conduit, so as to make useof reaction heat in the heat exchanging process. The term ‘middleportion’ preferably defines a region of the second conduit, which regionextends over about 50% of the total length of the second conduit andwhich is arranged around mid-length of the second conduit. However, acatalytically active element may also be arranged as far upstream as forexample to correspond to the position of the first conduit or tosubstantially directly correspond to the injection position for theexhaust gas.

A catalytically active element may be a catalytically active coating ofa section of a wall of the second conduit. A coating does not or notremarkably enhance the resistance of a fluid flow in the second conduit.In addition, a coating may be applied to a conduit wall before assemblyof the apparatus.

According to an aspect of the apparatus according to the invention, thecool fluid inlet and the hot gas outlet are arranged at one end portionof the apparatus and the cool fluid outlet, the hot gas inlet, theexhaust fluid inlet and the more than one openings are arranged at anopposite end portion of the apparatus. An end portion of the apparatusmay especially be a top portion of the apparatus and an opposite endportion of the apparatus may be a bottom portion of the apparatus.

By arranging inlets and outlets for the cool fluid and the hot gas onopposite end portions of the apparatus, the two fluids of the heatexchanging process are guided through the apparatus in a counter-flowdirection. This is a favorable flow direction in heat exchangers for amaximal heat transfer from the hot gas to the cool fluid. In addition,arranging inlets and outlets of conduits on opposite end portions, amaximal extension of the apparatus (at maximum the whole length of theheat conductive element) may be used for the heat exchanging process. Byarranging the exhaust fluid inlet and the more than one openings on thesame end portion of the apparatus than the hot gas inlet, a majority ofa length of the second conduit may be used for a mixing of the exhaustfluid and the hot gas, for oxidation of the mixture and for a heattransfer to the cool fluid.

By arranging inlets and outlets in top and bottom portions, the coolfluid and the hot gas or the mixture, respectively, essentially have atop-down and bottom-up flow direction. However, also a horizontal or anyother tilted flow direction is feasible with the apparatus according tothe invention.

An arrangement of inlets and outlets at end portions is not onlyfavorable for a counter-flow application as described above. Alsoco-flow or cross-flow arrangements may be preferred depending on theapplication. For example in a co-flow arrangement, hot gas and coolfluid essentially run parallel. Accordingly, in a co-flow arrangement atemperature of a heat conductive element between hot gas and cool fluidis rather uniform. This may be favorable to enable chemical reactions totake place on a large surface with about constant temperature.

The terms ‘end portion’ and ‘opposite end portion’, as well as ‘topportion’ and ‘bottom portion’ define regions of the apparatus accordingto the invention, which regions extend over one half (upper half, lowerhalf) of the apparatus and preferably define regions extending over onethird of the apparatus (uppermost third, lowermost third) starting atone end or an opposite end (bottom, top) of the apparatus and extend inthe direction of the middle of the apparatus. Therein, the apparatusdefines a longitudinal axis, which is arranged vertically in atop-bottom arrangement.

According to a further aspect of the apparatus according to theinvention, a wall of the second conduit comprises profile structures forsupporting a mixing of the exhaust fluid with the hot gas. Profilestructures may be used to cause a swirling effect in the second conduitthat supports the mixing of the exhaust fluid and the hot gas andtherefore may favorably influence the oxidation process of the exhaustfluid.

Profile structures may be surface structures of a wall or parts of awall of the second conduit. Profile structures may also be profiledwalls. Examples of profile structures are a rough surface, dips,indentations, fins or grooves on a surface or stamped wave-like or“chevron” pattern. Profile structures may also enlarge a surface of forexample a heat conductive element thus enhancing a heat exchanging.

According to an aspect of the apparatus according to the invention, theapparatus further comprises at least one further heat conductive plate,at least one further side plate and at least one further exhaust fluidinlet. The at least one further heat conductive plate and the at leastone further side plate are arranged in an alternating manner and form atleast one further first gap and at least one further second gap inbetween the side plates and the at least one further heat conductiveplate. At least one further second conduit is formed by the at least onefurther second gap. More than one further openings for introducing theexhaust fluid into the at least one further second conduit are arrangedwithin the maximum longitudinal extension for a heat exchanging processand at substantially a same longitudinal position with respect to thesecond conduit. The arrangement thereby forms a multiple-stack of heatexchanging and fluid mixing apparatuses.

The plate arrangement of the apparatus according to the invention allowsfor an easy extension of the apparatus to form a multiple-stack of heatexchanging and fluid mixing apparatuses arranged in parallel. Thereby,the same elements are stacked next to each other such that heatexchanging plates and side plates are arranged in alternating order.Also the gaps comprising the respective conduits are arranged inalternating order. By this a very compact arrangement of a plurality ofcombined mixers and heat exchangers may be manufactures. Inmultiple-stack apparatuses corresponding inlets and outlets arepreferably joined in respective collectors or manifolds. For example ina multiple-stack having a plurality of N hot gas outlets, the N hot gasoutlets are joined in one collector only. This simplifies the connectionof an apparatus according to the invention to other devices.

While the apparatus according to the invention may be manufactured in acost efficient manner, this cost efficiency is even more perceivable ifa multiple-stack of apparatuses according to the invention ismanufactured. Only two kinds of plates have to be manufactured, whichmay be formed by pressing or cutting. Also same further separatingelements may be used. Only one envelope is required for one apparatus ora multiple-stack of apparatuses combining heat exchanging and fluidmixing, since the fluid mixing is integrated into the heat exchanging.No assembly costs are required for connecting separate fluid mixers toheat exchangers, as the apparatus is manufactured as a single component.

The apparatus according to the invention is favourably used incombination and combined with a or with a plurality of fuel cells.Examples for such fuel cells are solid oxide fuel cells (SOFC), alkalifuel cells (AFC), molten carbon fuel cells (MCFC) and phosphoric acidfuel cells (PAFC). This combination is described by a solid oxide fuelcell (SOFC), as one exemplary type of fuel cells. SOFCs are favorablefor catalytic energy conversion due to their high efficiency. Since theyoperate at high temperatures (500-1000 degree Celsius), no previousreforming of fuel gases containing carbon to get hydrogen is necessarybefore the fuel gas may be used in the fuel cell. However, the oxidant,in general air or oxygen, needs to be preheated before being supplied tothe SOFC. Heat from the hot depleted air leaving the SOFC may further beused in the apparatus according to the invention with its heatexchanging function and cool fluid heated up in the apparatus accordingto the invention may directly be used as preheated air for the SOFC. Inaddition, the fuel remaining in the depleted fuel leaving the SOFC mayalso be used by connecting a depleted fuel outlet of the SOFC to theexhaust fluid inlet.

Accordingly, the respective inlets and outlets of the SOFC may beconnected to the respective inlets and outlets of the apparatusaccording to the invention. Therein, the cool fluid outlet of the firstconduit is connected to an air inlet of the solid oxide fuel cell and anair outlet of the solid oxide fuel cell is connected to the hot gasinlet of the second conduit. A depleted fuel outlet of the solid oxidefuel cell is connected to the exhaust fluid inlet. A cool fluid inletand a hot gas outlet of the apparatus according to the invention may notbe connected to another device or apparatus, but left open to theenvironment.

Especially in applications where the apparatus according to theinvention is connected with a device that has to reach a certainoperation temperature above ambient temperature, for example a fuel celloperating at elevated temperatures, an exhaust fluid may also be a fuelthat is not depleted. The reaction heat produced by for exampleoxidizing the fuel is exchanged with the cool fluid, which is heated upfast due to the higher energy density of fuel compared to depleted fuel.In conventional applications special start burners, for example gasburners or electric burners, are used to preheat a hot gas from 20 toabout 800 degrees Celsius, which hot gas may then be introduced into theheat exchanger. In combination with the apparatus according to theinvention, a small amount of (non-depleted) fuel may be used at thestart of an operation, such that start burners may be omitted, may havea simpler construction (less power required) or that regular startburners may be used for a reduced service time, for example for only afew minutes to preheat hot gas to a temperature of about 200 degreesCelsius only.

BRIEF DESCRIPTION OF FIGURES

In the following embodiments of the apparatus according to the inventionare shown by means of the enclosed drawings, wherein:

FIG. 1 shows an exploded view of an embodiment of the apparatus;

FIGS. 2,3,4 show further views of the embodiment of FIG. 1 withcollectors at inlets and outlets, wherein FIG. 2 is a front view througha plate stack as in FIG. 1, FIG. 3 is a longitudinal cut side view alonglines A-A, and FIG. 4 is an enlarged view of detail B of FIG. 3;

FIG. 5 is a sketch of another embodiment of the apparatus;

FIG. 6 is a cross sectional view of the embodiment of FIG. 5;

FIG. 7 shows a simulation of a fluid introduced into hot gas through arow of openings in a heat exchanging plate.

DETAILED DESCRIPTION

In FIG. 1 an embodiment of a plate heat exchanger and fluid mixer isshown. Three plates 1,2,3 are arranged next to each other in a face toface manner. The plates are distanced by spacers 41,42,43,51 forminggaps 4,5 in between the plates 1,2,3. A first gap 4 is formed betweenthe first plate 1 and the second (middle) plate 2 and a second gap 5 isformed between the second plate 2 and the third plate. Second gap 5forms a second conduit 55 provided for guiding a hot gas (the flowdirection of the hot gas is indicated by dark arrows 56), for examplehot air, through second conduit 55. First gap 4 is divided by a spacer43 into an upper section and a lower section. The upper section of thefirst gap 4 forms a first conduit 44 provided for guiding a cool fluid(the flow direction of the cool fluid is indicated by long light arrows49), for example cool air, through the first gap 4. The second plate 2is a heat conductive plate comprising or made of a heat conductivematerial for transferring heat from the hot gas guided in the secondconduit 55 to the cool fluid guided in the first conduit 44. The lengthL of the heat conductive plate 2 defines a maximum longitudinalextension 22 for a heat exchanging process in the apparatus. Thisarrangement works as a heat exchanger.

The lower section of the first gap 4 forms a third conduit 45. Thespacer 43 separating the third conduit is preferably horizontallyarranged and extends over the whole width W of the heat conductive plate2. This spacer 43 is arranged such as to preferably form a gas-tight andfluid-tight separation between first and third conduit 44, 45. The thirdconduit 45 is provided for guiding an exhaust fluid (the flow directionof the exhaust fluid is indicated by small arrows 42), for example anexhaust gas or a depleted fuel.

The heat conductive plate 2 is provided with a plurality of openings 21,for example a line of perforations. This line preferably extends alongthe length of the third conduit 45, which corresponds to the width W ofthe heat conductive plate 2. The openings 21 are arranged in a row at asame longitudinal position of the embodiment of FIG. 1. This correspondsto the same longitudinal position of the second conduit 55 such thatexhaust gas 42 is introduced into the second conduit 55 at a samelongitudinal position or—due to the second conduit being a straightconduit,—a length of the second conduit 55 measured from a hot gas inlet52. Injected exhaust gas 42 reaches the region which is cooled by thecool fluid and the catalytically active section 54 at substantially thesame time after injection, independent of which opening 21 the exhaustgas 42 is injected. By this, a controlled injection of exhaust gas intothe hot gas of the second conduit 55 may be provided. The openings 21are preferably evenly distributed across the width W, support an evenand thorough mixing of the exhaust fluid with the hot gas, which furthersupports a controlled chemical reaction and heat exchange in theapparatus according to the invention.

The exhaust fluid enters the third conduit 45 by an exhaust fluid inlet46 arranged in the bottom portion of the apparatus and in a front sideof the first gap 4 (with respect to FIG. 1). The exhaust fluid leavesthe third conduit 45 through the plurality of openings 21 in the heatconductive plate 2 and enters the second conduit 55. The exhaust fluidmixes with the hot gas flowing in the second conduit (this mixing isindicated by the dark arrows 56 turning to light arrows). The hot gasenters the second conduit 55 by a hot gas inlet 52 and flows to the topside of the apparatus to the hot gas outlet 53. The hot gas—nowcooled—and any reaction products as there may be, for example water,carbon dioxide etc., leave the second conduit 55 by the hot gas outlet53.

The hot gas inlet 52 is arranged in the bottom side of the apparatus andessentially extends over the whole width of the bottom side. The hot gasoutlet 53 is arranged in the top side of the apparatus and essentiallyextends over the whole width of the top side.

The exhaust fluid inlet 46 and the plurality of openings 21 are arrangedin the bottom portion of the apparatus. By this the mixing of exhaustfluid with hot gas starts at one end portion of the apparatus and theexhaust fluid/hot gas mixture is guided along most of the length of thesecond conduit 55. Therein, most of the surface of the heat exchangingplate 2 may be used for a heat exchange from hot gas to cool fluid viaheat exchanging plate and most time that the mixture spends in thesecond conduit 5 may be used for a chemical reaction, preferably anexothermic chemical reaction such as an oxidizing process.

In order to ensure that an exhaust fluid is oxidized, for example if thetemperature of the hot gas is not sufficient to start or maintain anoxidizing reaction, the second conduit 55 is provided with acatalytically active section 54, for example a catalytically activecoating on the surface of the third plate 3. This catalytically activesection 54 is arranged downstream (with respect to the flow direction ofthe hot gas) of the plurality of openings 21. Preferably, thecatalytically active section 54 extends over a middle portion of thesecond conduit 55, such as to allow for a thorough mixing and still makeuse of the reaction heat produced by the oxidizing reaction of theexhaust fluid in the heat exchanging process.

The cool fluid enters the first conduit 4 by a cool fluid inlet 47arranged in a top portion of the apparatus and in a rear side of thefirst gap 4 (with respect to FIG. 1). The cool fluid is heated up duringits flowing through the first conduit 44 by the heat provided by theheat conductive plate 2, which is heated up by the hot gas guided in thesecond conduit 55 on the other side of the heat conductive plate 2. Thecool fluid,—which is named cool fluid before entering and after leavingthe heat exchanging and fluid mixing apparatus for simplicity reasons—isheated for example to a few hundred degrees Celsius. It leaves the firstconduit 44 by a cool fluid outlet 48 arranged in the bottom portion andin the front side of the apparatus (with respect to FIG. 1). This heatedcool fluid may further be used, for example as heat source inair-conditioning or—as in preferred embodiments—as a preheated airsource for a fuel cell.

An upstream end of the catalytically active element 54 may directlycorrespond to a most downstream longitudinal position of the firstconduit 44. By this, a reaction in the second conduit 55 is controlledby its initiation or further support at a specific longitudinal positionin the apparatus. In addition, the reaction heat is directly led away bythe cool fluid in the first conduit. That is, no excessive heat isproduced in the second conduit, which is not led away directly and alsoin a controlled manner.

In FIGS. 2 to 4 the apparatus of FIG. 1 in a mounted state includingcollectors 47-61 at the inlets and outlets is shown. Same referencenumbers as in FIG. 1 are used for the same or similar features.

In FIG. 1 and FIG. 2 all inlets and outlets are arranged within themaximum longitudinal extension 22 for a heat exchange (hot gas inlet andoutlet are arranged at the outermost end of the extension 22). In FIGS.2 and 3 a hot gas inlet collector 58 and hot gas outlet collector 57 isarranged adjacent the maximum longitudinal extension 22 with respect tothe longitudinal direction of the apparatus, for example upstream ordownstream of the extension 22 with respect to the hot gas flow. Suchcollectors are favourably used for an apparatus built as multiple-stack.For example an apparatus according to the invention having a plurality Nof second conduits 55 also comprises a plurality of N hot gas outlets53. However, the plurality of N hot gas outlets 53 is brought togetherat the one hot gas outlet collector 57. The same may equally be adaptedto the hot gas inlets 52, cool fluid inlets 47 and cool fluid outlets48, as well as exhaust fluid inlets 46. Therein, the number N of theplurality of second conduits, a number M of a plurality of firstconduits and a number L of a plurality of third conduits may be equal ordiffer from each other.

The through view of the apparatus in FIG. 2 shows the flows of theindividual fluids. The hot gas—indicated by dark arrows 56—enters theapparatus at the hot gas inlet collector 58 arranged over the wholebottom side of the apparatus and slightly outside or upstream of themaximum longitudinal extension 22, flows upwardly and leaves theapparatus at the hot gas outlet collector 57, which is also arrangedover the whole top side of the apparatus and slightly outside ordownstream of the maximum longitudinal extension 22. The coolfluid—indicated by light arrows 49 enters the apparatus at the coolfluid inlet collector 59, which is arranged in the top portion of theapparatus on one side of the apparatus (left side in FIG. 2) just belowthe hot gas outlet collector 57 and within the maximum longitudinalextension 22. A spacer 41 closes off the first conduit 44 versus the topof the apparatus. The cool fluid flows downwardly and leaves theapparatus at the cool fluid outlet collector 60 arranged on the oppositeside of the apparatus (right side in FIG. 2) in the bottom portion ofthe apparatus and within the maximum longitudinal extension 22. The coolfluid outlet collector 60 is arranged above and distanced from theexhaust fluid inlet collector 61 by the distance of spacer 43. Theexhaust fluid inlet collector 61 is arranged on the same side of theapparatus (right side in FIG. 2) as the cool fluid outlet collector 60and within the maximum longitudinal extension 22, but might also bearranged in the bottom portion but on the side of the cool fluid inletcollector 59.

As shown in FIG. 4, which is an enlarged view of detail B of FIG. 3,which itself is a cross section along line A-A of FIG. 2—shown for asingle stack only for the sake of clarity—, the exhaust fluid flows inthe third conduit 45 formed between the first plate 1 and the heatconductive plate 2 and upper and lower spacers 43,41. The exhaust fluidpasses through the plurality of openings 21, which are arranged in oneline and at a same longitudinal position or length in the heatconductive plate. The exhaust fluid then enters the second conduit 55,mixes with the hot gas and passes the catalytically active section 54.Oxidation products leave the apparatus together with the hot gas throughthe hot gas outlet 53 or hot gas outlet collector 57, respectively.

Guiding the exhaust fluid on the side of the cool fluid is favourablebecause the flow of hot gas in the second conduit remains undisturbed.Since hot gas generally has a very low density, obstructions in the flowpath may cause an unwanted pressure drop over the hot gas conduit.

The inlets and outlets of the conduits end in collectors and arerealized in this embodiment as interfaces extending upwardly andoutwardly of the basically rectangular plates 1,2,3 that form the heatexchanger body. Such interfaces simplify the connection to correspondinginlets and outlets of for example an energy converter such as a fuelcell or other devices the apparatus according to the invention may beconnected to.

In FIGS. 5 and 6 another embodiment of the apparatus according to theinvention is shown, wherein the third conduit 45′ is arranged in thesecond conduit 55′ guiding the hot gas. The apparatus is arranged in ahorizontal position, such that a cool fluid/hot gas flow for the heatexchanging process occurs in a counter-flow left-right/right-leftdirection along a length of the rectangular plates. Again, samereference numbers are used for same or similar features. Broad darkarrows 56 indicate hot gas flow, narrow dark arrows 49 indicate coolfluid flow and small arrows 42 indicate exhaust fluid flow.

In this embodiment a heat exchanging process from the hot gas to thecool fluid through contact with the heat conductive plate 2′ takes placeover the maximum longitudinal extension 22. It takes place over thewhole length L of the heat conductive plate since hot gas inlet andoutlet 52,53 with corresponding collectors 58,57, as well as cool fluidinlet and outlet 47,48 with corresponding collectors 60′,59 are arrangedat the ends of the maximum longitudinal extension 22.

The exhaust fluid inlet collector 61′ or the at least one exhaust fluidinlet 46, is arranged near mid-length of the apparatus or near half thelength L of the heat conductive plate 2′. The third conduit 45′ isintegrated into the second conduit (seen in FIG. 6) and extends over thewidth of second conduit 55′ and the width W of the heat conductive plate2′. The third conduit 45′ is arranged perpendicular to the secondconduit 55′ and extends over about half the width of the second gap 5between the heat conductive plate 2′ and the second side plate 3. In theother half of the width of the second gap the hot gas flows past thethird conduit 45′. The third conduit 45′ is provided with a plurality ofopenings 21′ along the length of the third conduit, arranged on adownstream side with respect to the second conduit and at a samelongitudinal position. By this exhaust fluid in the third conduit mayleave the third conduit and enter the hot gas in the second conduit 55′at several locations across the width of the second conduit. The thirdconduit forms an obstacle in the path of the hot gas and causes the hotgas and the exhaust fluid to swirl, which additionally supports themixing of the two fluids. For optimizing a pressure drop in the secondconduit, the third conduit may also be limited in length, i.e. notextend over the whole width W of the second conduit. Hot gas in thesecond conduit then bypasses the injection and mixing area.

Since no exhaust fluid needs to pass through the heat conductive plate2′, no openings are provided therein.

The cool fluid outlet 48 and cool fluid outlet collector 59 is arrangedat one end (right side in FIG. 5) of the apparatus. Thereby, the lengthof the first conduit 44′, where cool fluid is guided in, is enlarged tothe whole length of the heat conductive plate 2′, enhancing theefficiency of the heat exchanging process.

Arranging the third conduit in the second conduit guiding the hot gas ina more central position of the second conduit allows the arrangement ofan injection and mixing of exhaust fluid in a position of the apparatuswith lower temperature than at the hot gas inlet. If temperatures at thehot gas inlet are very high, rapid oxidation of the exhaust fluid mayalready occur at the hot walls of the second conduit, thus furtherraising the temperatures. By arranging the third conduit furtherdownstream of the hot gas inlet an oxidation temperature may be chosenand adapted to a corresponding application of the apparatus according tothe invention. Especially, the apparatus according to the invention maybe used in more extreme conditions, such as higher initial temperaturesof the hot gas.

It can be seen, that an exhaust fluid inlet may also be arranged in thesecond conduit at the same longitudinal position than the hot gas inletat the one end of the heat conductive plate 2′, i.e. at the one end ofthe maximum longitudinal extension 22. In such an arrangement, the morethan one openings for introducing the exhaust fluid into the secondconduit may be identical to the exhaust fluid inlet.

In FIG. 6 the apparatus is shown as multiple-stack. A further heatconducting plate 200 and a further side plate 300 is stacked on top ofthe stack of plates 2′,3 (lowermost side plate 1 not shown) of a basicstack for example as shown in FIG. 1. Corresponding further first andsecond gaps are formed. A further third conduit 450′ provided withopenings 21′ is arranged in the further third conduit 45′.

Also the apparatus as shown in FIGS. 1 to 3 may be extended to amultiple stack of heat exchanging and fluid mixing apparatuses. Thereinfurther heat exchanging plates having openings are provided and furtherspacers are arranged in respective locations.

In FIG. 7 a simulation of a fluid introduced into hot gas throughopenings 21 in a heat exchanging element, preferably a plate, is shown.The simulation shows the example of an anode gas containing hydrogen andother components such as CO, CO2 and water. The anode gas is introducedinto a cathode gas, which is at a temperature of 700 degree Celsius. Thecathode gas contains oxygen, N2 and water. The water is provided in theform of steam or vapour. At these temperatures and at a givenconcentration of hydrogen and oxygen used for the simulation, ignitionof the gas mixture starts after 5 ms after introduction of the anode gasinto the cathode gas. In the figure, streamlines 66 representing the gasflow are depicted in grey shades, which shades change from the point ofinjection 21 with time (dark at injection 21; dark after 5 ms). Thestreamlines 66 end after 5 ms after injection. Depending on the kind ofspreading of the gas flow after its injection and turbulences, a flowadvances further downstream into the apparatus as is indicated by thedifferent lengths of streamlines 66. A flow direction is indicated byarrow 69.

Line 64 indicates the arrangement of the cool conduit at a locationdownstream of the openings 21 and on the opposite side of the heatexchanging element than the cathode gas. That is, line 64 indicates thesection of the apparatus, where the hot cathode gas now mixed with theanode gas starts to get cooled via the heat exchanging element.Accordingly, the position of the cool conduit may be chosen such as tobe optimized on the temperature and other parameters of the reaction tobe performed in the apparatus. In the present example, the cool conduitis arranged such as to correspond to a distance that the introduced flowreaches at or preferably after 5 ms after injection of the anode gas. Bythis no combustion occurs without cooling. Preferably line 64 alsoindicates the upstream end of a catalytically active coating in the hotconduit. The catalytically active coating is arranged preferably suchthat ignition only starts at the catalytically active heat exchangerregion.

It can be seen in FIG. 7 that most streamlines 66 reach line 64 when orshortly before 5 ms have passed after the time of injection. At thismoment the gas reaches the section, where the gas is cooled by thecooling fluid. At the same time the gas would start combusting, whichcombustion reaction is additionally supported or induced by thecatalytically active coating that starts in this area. However, due tothe cooling action, the chemical process becomes rather a quiteoxidation reaction than a combustion. By this, excessive heat caused bythe oxidation reaction is used and led away in the heat exchanger. Nouncontrolled reaction occurs that might possibly damage the apparatus.The coating additionally supports the controlled combustion of the gasmixture.

The invention has been described with reference to the embodiments shownin the drawings. However, it is obvious to a person skilled in the artthat many variations, modifications or changes are possible withoutdeparting from the scope of the invention. By way of example only, thearrangement of inlets and outlets may vary. For example the inlets,outlets and collectors may be arranged differently, also for exampleperpendicular to side plates. Also, the manner how the conduits areembodied may be different from the conduits actually shown in thedrawings. All such variations, modifications or changes are intended tobe within the scope of the invention which is defined by the appendedclaims.

1. Combined heat exchanging and fluid mixing apparatus comprising: afirst conduit for guiding a cool fluid through the first conduit, thefirst conduit comprising a cool fluid inlet and a cool fluid outlet; asecond conduit for guiding a hot gas through the second conduit, thesecond conduit comprising a hot gas inlet and a hot gas outlet; a heatconductive element arranged between the first conduit and the secondconduit for transferring heat from the hot gas to the cool fluid, theheat conductive element having a length defining a maximum longitudinalextension for a heat exchanging process in the apparatus, the apparatusfurther comprising a third conduit for guiding an exhaust fluid, thethird conduit comprising an exhaust fluid inlet arranged at one end ofthe third conduit for introducing the exhaust fluid into the apparatusfor mixing of the exhaust fluid with the hot gas and for a chemicalreaction of the so formed exhaust fluid/hot gas mixture in the secondconduit, wherein the third conduit is provided with more than oneopenings for passing the exhaust fluid from the third conduit into thesecond conduit, wherein the more than one openings for introducing theexhaust fluid into the second conduit are arranged within the maximumlongitudinal extension for a heat exchanging process in the apparatus,and wherein the more than one openings are arranged at substantially asame longitudinal position with respect to the second conduit. 2.Apparatus according to claim 1, wherein the exhaust fluid inlet isarranged within the maximum longitudinal extension for a heat exchangingprocess in the apparatus.
 3. Apparatus according to claim 1, wherein themore than one openings are arranged downstream of the hot gas inlet. 4.Apparatus according to claim 1, wherein the third conduit is arranged ina direction perpendicular to a direction of the first or second conduit.5. Apparatus according to claim 1, wherein the first conduit and thethird conduit are arranged on a same side of the heat conductiveelement, and the more than one openings is arranged in the heatconductive element.
 6. Apparatus according to claim 5, wherein afluid-tight separation element is arranged between the first conduit andthe third conduit for a fluid-tight separation of the first conduit andthe third conduit.
 7. Apparatus according to claim 1, wherein the secondconduit and the third conduit are arranged on a same side of the heatconductive element.
 8. Apparatus according to claim 5, wherein the heatconductive element is a heat conductive plate arranged between a firstand a second side plate, the heat conductive plate and the first andsecond side plates being arranged at a distance to each other forming afirst gap between the first side plate and the heat conductive plate andforming a second gap between the heat conductive plate and the secondside plate, wherein the first gap is separated into the first conduitand into the third conduit, wherein the second conduit is formed by thesecond gap, and wherein the more than one openings is arranged in theheat conductive plate.
 9. Apparatus according to claim 1, wherein theheat conductive element is a heat conductive plate arranged between afirst side plate and a second side plate, the heat conductive plate andthe first and second side plates being arranged at a distance to eachother forming a first gap between the first side plate and the heatconductive plate and forming a second gap between the heat conductiveplate and the second side plate wherein the first conduit is formed bythe first gap and the second conduit is formed by the second gap whilethe third conduit is arranged in the second conduit.
 10. Apparatusaccording to claim 1, wherein the more than one openings are arrangedalong a length of the third conduit
 11. Apparatus according to claim 1,wherein the second conduit comprises a catalytically active element forfurther chemical reaction such as oxidation of the exhaust fluid/hot gasmixture.
 12. Apparatus according to claim 1, wherein the second conduitcomprises a catalytically active element for further chemical reactionsuch as oxidation of the exhaust fluid/hot gas mixture.
 13. Apparatusaccording to claim 1, wherein the cool fluid inlet and the hot gasoutlet are arranged at one end portion of the apparatus; and the coolfluid outlet, the hot gas inlet, the exhaust fluid inlet and the morethan one openings are arranged at an opposite end portion of theapparatus.
 14. Apparatus according to claim 1, wherein a wall of thesecond conduit comprises profile structures for supporting a mixing ofthe exhaust fluid with the hot gas.